This invention relates generally to ocular implants and more specifically to a modular ocular implant with an adjustable and replaceable lens.
A cataract is a condition where a normally clear lens of the eye becomes progressively opaque. The opacification generally occurs over a period of time and the amount of light which passes through the lens decreases thereby decreasing vision. It is necessary, therefore, to surgically remove and replace the clouded lens. Often, there is a coexistent refractive defect such as myopia (short sightedness), hyperopia and astigmatism.
Generally the lens is removed for cataract or clear lens refractive purposes for high myopia and hyperopia, and is replaced at the time of surgery with an intraocular lens formed from a biocompatible material such as PMMA (polymethyl methacrylate) or the like. The surgeon makes an incision in the sclera and cornea to allow the removal of the semi-opaque lens and/or clear lensectomy and insertion of the implant. The typical prior art lens implant is either of plano-convex design or double convex design, with each curved surface defining a spherical section. A large number of patients will have significant post-surgical astigmatism and spherical error and will need a spherical/astigmatic adjustment in their glasses. The surgery can induce astigmatism which can fluctuate greatly over time after surgery, as can the lens capsule (bag), zonules, etc.
One problem associated with intraocular lens implants is that it is necessary to decide, preoperatively, on the power of the lens. This can be done by performing various standard (ultrasound) procedures such as a preoperative refraction and keratometric determinations and then making an estimate of the proper power of lens to determine proper refraction of the eye. Although the ophthalmologist uses the best techniques available, it is very difficult to accurately predict, preoperatively, the optimal power for the lens implant because of multiple variables of axial length, anterior chamber depth, corneal curvature and size, growth of the eye (pediatric cases), irregular post scleral surfaces (usually seen in the macular area) such as myopic staphylomas, mismeasurement and mislabeling of the IOL power and other human errors. Therefore, most patients are required to use glasses for precise focusing even after the replacement of the semi-opaque lens. Further, since the exact amount and axis of astigmatism cannot be accurately determined until several weeks after surgery, the patient may require glasses for best vision and the lens prescription may have to be changed more than once as the eye heals over time, because of different visual needs.
Several intraocular lenses which allow post-surgical correction are known. U.S. Pat. No. 4,575,373 discloses a laser adjustable intraocular lens. U.S. Pat. No. 4,816,031 provides a lens implant with a second soft and pliable lens position over it and electromechanical circuitry for regulating the distance between the two lenses.
U.S. Pat. No. 4,601,545 discloses a variable power lens having optically active molecular material, such as liquid crystals than can be configured using electrical voltages. U.S. Pat. No. 4,564,267 discloses a variable focal length lens which can be electrically controlled by applying an electric field to a compound lens with one lens formed of electrooptic crystals.
U.S. Pat. No. 4,373,218 discloses a variable power intraocular lens including a fluid expandable sac for containing a liquid crystal material that responds to electric charge to change the index of refraction of the lens.
U.S. Pat. No. 4,932,966 discloses a intraocular lens apparatus having a flexible lens member and with a relatively rigid portion with fluid-filled chambers therebetween. The shape or position of the lens portion is adjusted by changing fluid pressure in the fluid-filled chambers.
U.S. Pat. No. 4,932,971 provides a clip-on optic assembly for clipping in situ onto a previously implanted intraocular lens to change its optical characteristics without removal from the eye.
U.S. Pat. No. 5,108,429 provides an adjustable focus lens with a plurality of micromotor devices spaced around the periphery of the lens body, the devices being responsive to an external control signal for selectively changing the position of a lens body. U.S. Pat. No. 5,203,788 also provides an adjustable lens apparatus having a lens body with a relatively rigid outer ring with micromotors between the lens body and the outer ring that are responsive to outside actuation.
U.S. Pat. No. 5,171,266 discloses an intraocular lens having a flexible lens body center portion surrounded by an outer ring which is sensitive to an external force such as a magnetic force. The shape of the outer body can be changed by magnetic force to elongate the lens body. U.S. Pat. No. 5,326,347 also discloses an intraocular implant that is responsive to the post-surgical application of force, such as the movement of the implantee's head and magnetic force to change the focus.
Although the foregoing devices may solve the problem of adjustment of the lens post-surgically, there have other inherent drawbacks. Some of the adjustable lens are complicated in design employing power sources, micromotors, microfluid pumps and electric or electrochemical circuitry. Such complex devices can be expensive to manufacture and relatively bulky or heavy in use. Some adjustable lenses require the use of external adjustment technology such as electric current, magnets or other forces.